How to know the speed and motion vector of the mouse pointer?

I'm starting to learn C # and I want to practice with vectors. I made a WPF application in which circles are created on PKM, and if you press and hold the LMB, they can be moved and when released, they should continue to move at the speed of the mouse pointer. I can't do it so that they continue to move at the right speed, it does not change. How can I find out the pointer speed? PS I tried to find out the vector by saving the previous coordinate and subtracting it from the past.

// при отпускании мыши Vector mousemove = new Vector(Mouse.GetPosition(main).X - lastpos.X, Mouse.GetPosition(main).Y - lastpos.Y); elipse[i].direction = mousemove / mousemove.Length; // elipse - класс, содержащий круг (Elipse) и вектор его движения (direction) //в таймере lastpos = new Point(Mouse.GetPosition(main).X, Mouse.GetPosition(main).Y);